III. — Meteorological, etc., Observations. 



found to a greater or less extent in the atmosphere. In the forimdu which 

 serves for the calculation of the altitudes (.sea p. .'iGL') there occurs the factor 



1 - 378 rh ^^'^^'"^ '^ ^'^ '■^^ mean vapotir tension at the two stations, and 7 the 



'/ 

 m^au of the pressures, and this factor has reference to the influence exercised 

 by the presence of the aqueous vapour on the readings of barometric altitudes. 

 For Bujongolo the vapour ten.sion is known, l>ut not for the observed places 

 on Ruwenzori, as here no psychrometric ol3sei'\-ations were made. 



The neglect of the factor relating to the humidity might be a cause of 

 error, to eliminate which, at least partly, a mean humidity of aliout 60 has been 

 admitted for the stratum of the air comprised lietween Bujongolo and the 

 observed station.* 



This humidity of 60 is certainly less than the true mean, since at 

 Bujongolo the humidity i.s always very high (mean 89), and there is reason 

 to believe that it is always considerable in the other places too, where cloiifly, 

 foggy and rainy weather prevail. 



On the Tables IX, X, XI and XII are recorded the altitudes of the various 

 other places on Ruwenzori, calculated with the previously indicated iwrmtf. 



Regarding the results olitaincd, it may lie noticed that the determinations 

 made with the mercurial baiometer were found to agree sufficiently well with 

 each other whenever it was possible to make more than one determination for 

 any given place, and they agree also with the surveys made with geodetic 

 methods. 



Owing to the irregular behaviour of the aneroid barometers, the measure- 

 ments taken with these instruments present a far less degree of approximation. 



* 'J'o sliow Ihe possible influence of such a correction, reference may be made to (he 

 special ease of the Margherita Peak. Here the pressure at 11 o'clock on 18th June was 

 414'0 mm and the tempeniture — 3°-3 Celsius (20°'6 F.), whereas at Bujongolo, at 12 o'clock 

 on the same day, the pressure was 4879 mm. and the temperature o'l Celsius (11' F.), 

 hence the mean pressure was about 451 mm. and the mean temperature 0°-9 Celsius (33° F.). 

 Had the air been saturated at this temperature the vapour tension would liave been 487 mm. 

 Admitting a humidity of GO the tension falls to 2'92 mm., with wliieh datum, and wit)i the 

 mean pressure of 4.51, we get the cologarithm of tlu> term of correction for the iiumidify, 

 namely : 



colog. L_^ = 000103 



1-0 378'*' 



n 



Without taking account of the humidity, the height of Margherita Peak above Bujongolo 

 was found to be 1,324 metres; with this added it becomes 1,327 metres, that is to say, we 

 have a rise of about 0-22 per i-ent. Admitting a humidity of 80 the height would become 

 1,328'5 metres, with a rise of 0'33 per cent. 



367 



